Lithium anodes for electrochemical cells

ABSTRACT

Provided is an anode for use in electrochemical cells, wherein the anode active layer has a first layer comprising lithium metal and a multi-layer structure comprising single ion conducting layers and polymer layers in contact with the first layer comprising lithium metal or in contact with an intermediate protective layer, such as a temporary protective metal layer, on the surface of the lithium-containing first layer. Another aspect of the invention provides an anode active layer formed by the in-situ deposition of lithium vapor and a reactive gas. The anodes of the current invention are particularly useful in electrochemical cells comprising sulfur-containing cathode active materials, such as elemental sulfur.

RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S.application Ser. No. 09/864,890, filed May 23, 2001, which is acontinuation-in-part of U.S. application Ser. No. 09/721,578, filed 21Nov. 2000 (now U.S. Pat. No. 6,797,428), and U.S. application Ser. No.09/721,519, filed 21 Nov. 2000 (now U.S. Pat. No. 6,733,924); both ofwhich claim priority to U.S. Provisional Patent Application Ser. No.60/167,171, filed 23 November 1999, the disclosures of which areincorporated herein by reference in their entirety for all purposes.

TECHNICAL FIELD

The present invention relates generally to the field of lithium anodesfor use in electrochemical cells. More particularly, the presentinvention pertains to an anode for use in an electrochemical cellcomprising an anode active layer comprising lithium metal in contactwith a multilayer structure comprising three or more layers interposedbetween the anode active layer and a non-aqueous electrolyte. Thepresent invention also pertains to methods of forming such anodes,electrochemical cells comprising such anodes, and methods of making suchcells.

BACKGROUND

Throughout this application, various publications, patents, andpublished patent applications are referred to by an identifyingcitation. The disclosures of the publications, patents, and publishedpatent specifications referenced in this application are herebyincorporated by reference into the present disclosure to more fullydescribe the state of the art to which this invention pertains.

There has been considerable interest in recent years in developing highenergy density batteries with lithium containing anodes. Lithium metalis particularly attractive as the anode of electrochemical cells becauseof its extremely light weight and high energy density, compared forexample to anodes, such as lithium intercalated carbon anodes, where thepresence of non-electroactive materials increases weight and volume ofthe anode, and thereby reduces the energy density of the cells, and toother electrochemical systems with, for example, nickel or cadmiumelectrodes. Lithium metal anodes, or those comprising mainly lithiummetal, provide an opportunity to construct cells which are lighter inweight, and which have a higher energy density than cells such aslithium-ion, nickel metal hydride or nickel-cadmium cells. Thesefeatures are highly desirable for batteries for portable electronicdevices such as cellular phones and laptop computers where a premium ispaid for low weight. Unfortunately, the reactivity of lithium and theassociated cycle life, dendrite formation, electrolyte compatibility,fabrication and safety problems have hindered the commercialization ofcells with lithium anodes.

The separation of a lithium anode from the electrolyte of the cell isdesirable for reasons including the prevention of dendrites duringrecharging, reaction with the electrolyte, and cycle life. For example,reactions of lithium anodes with the electrolyte may result in theformation of resistive film barriers on the anode. This film barrierincreases the internal resistance of the battery and lowers the amountof current capable of being supplied by the battery at the ratedvoltage.

Many different solutions have been proposed for the protection oflithium anodes including coating the lithium anode with interfacial orprotective layers formed from polymers, ceramics, or glasses, theimportant characteristic of such interfacial or protective layers beingto conduct lithium ions. For example, U.S. Pat. Nos. 5,460,905 and5,462,566 to Skotheim describe a film of an n-doped conjugated polymerinterposed between the alkali metal anode and the electrolyte. U.S. Pat.No. 5,648,187 to Skotheim and U.S. Pat. No. 5,961,672 to Skotheim et al.describe an electrically conducting crosslinked polymer film interposedbetween the lithium anode and the electrolyte, and methods of making thesame, where the crosslinked polymer film is capable of transmittinglithium ions. U.S. Pat. No. 5,314,765 to Bates describes a thin layer ofa lithium ion conducting ceramic coating between the anode and theelectrolyte. Yet further examples of interfacial films for lithiumcontaining anodes are described, for example, in: U.S. Pat. Nos.5,387,479 and 5,487,959 to Koksbang; U.S. Pat. No. 4,917,975 to DeJonghe et al.; U.S. Pat. No. 5,434,021 to Fauteux et al.; and U.S. Pat.No. 5,824,434 to Kawakami et al.

A single protective layer of an alkali ion conducting glassy oramorphous material for alkali metal anodes, for example, inlithium-sulfur cells, is described in U.S. Pat. No. 6,025,094 to Viscoet al. to address the problem of short cycle life.

Despite the various approaches proposed for methods for forming lithiumanodes and the formation of interfacial or protective layers, thereremains a need for improved methods, which will allow for increased easeof fabrication of cells, while providing for cells with long cycle life,high lithium cycling efficiency, and high energy density.

SUMMARY OF THE INVENTION

The anode of the present invention for use in an electrochemical cellcomprises: (i) a first anode active layer comprising lithium metal; and(ii) a multi-layer structure in contact with a surface layer of thefirst anode active layer; wherein the multi-layer structure comprisesthree or more layers, wherein each of the three or more layers comprisesa layer selected from the group consisting of single ion conductinglayers and polymer layers. In one embodiment, the multi-layer structurecomprises four or more layers.

The anode active layers of the present invention may further comprise alayer of a temporary protective material in contact with a surface ofthe first anode active layer, and interposed between the anode activelayer and the multilayer. Examples of temporary protective layersinclude, but are not limited to temporary metal layers, and intermediatelayers formed from the reaction of a gaseous material with the lithiumsurface, such as plasma CO₂ treatments. The temporary metal layer iscapable of forming an alloy with lithium metal or is capable ofdiffusing into lithium metal.

The anodes may further comprise a substrate, wherein the substrate is incontact with a surface of the first layer on the side opposite to themulti-layer structure, or temporary protective layer. Preferable, thesubstrate is selected from the group consisting of metal foils, polymerfilms, metallized polymer films, electrically conductive polymer films,polymer films having an electrically conductive coating, electricallyconductive polymer films having an electrically conductive metalcoating, and polymer films having conductive particles dispersedtherein. Polymer films are especially preferred because of their lightweight.

The single ion conducting layer of the anode of the present inventionpreferably comprises a glass selected from the group consisting oflithium silicates, lithium borates, lithium aluminates, lithiumphosphates, lithium phosphorus oxynitrides, lithium silicosulfides,lithium germanosulfides, lithium lanthanum oxides, lithium tantalumoxides, lithium niobium oxides, lithium titanium oxides, lithiumborosulfides, lithium aluminosulfides, and lithium phosphosulfides andcombinations thereof.

The polymer layer of the anode of the present invention may be selectedfrom the group consisting of electrically conductive polymers, ionicallyconductive polymers, sulfonated polymers, and hydrocarbon polymers. In apreferred embodiment the polymer layers comprise a crosslinked polymer.In one embodiment, the polymer layer of the multi-layer structurecomprises a polymer layer formed from the polymerization of one or moreacrylate monomers selected from the group consisting of alkyl acrylates,glycol acrylates, and polyglycol acrylates.

The multi-layer structure of the anode may further comprise a metalalloy layer. In one embodiment, the metal alloy layer preferablycomprises a metal selected from the group consisting of Zn, Mg, Sn, andAl. Such a layer is interposed between the other layers of themulti-layer structure or may form the outer layer of the structure.

Another aspect of the present invention pertains to methods for forminganodes according to the present invention. The layers of the anode ofthe present invention may be deposited by any of the methods, such as,but not limited to physical deposition methods, chemical vapordeposition methods, extrusion, and electroplating. Deposition ispreferably carried out in a vacuum or inert atmosphere.

Still another aspect of the anodes of the present invention pertains tomethods to deposit in-situ on a substrate anode-active layers comprisinglithium co-deposited with a gaseous material, such as, for example, CO₂or acetylene (C₂H₂).

Anodes of the present invention are suitable for use in both primary orsecondary cells. In one embodiment, the present invention provides anelectrochemical cell comprising: (a) a cathode comprising a cathodeactive material; (b) an anode; and (c) a non-aqueous electrolyteinterposed between the anode and the cathode, wherein the anodecomprises: (i) a first anode active layer comprising lithium metal, asdescribed herein; and (ii) a multi-layer structure, as described herein,in contact with a surface layer of the first layer; wherein themulti-layer structure comprises three or more layers wherein each of thethree or more layers comprises a layer selected from the groupconsisting of single ion conducting layers and polymer layers. Theelectrolyte is selected from the group consisting of liquidelectrolytes, solid polymer electrolytes, and gel polymer electrolytes.In one embodiment, the non-aqueous electrolyte is a liquid. In oneembodiment, the electrolyte comprises a separator selected from thegroup consisting of polyolefin separators and microporous xerogel layerseparators. The cathode active material may comprise one or morematerials selected from the group consisting of electroactive metalchalcogenides, electroactive conductive polymers, and electroactivesulfur-containing materials, and combinations thereof. In oneembodiment, the cathode active material comprises electroactivesulfur-containing materials, as described herein.

As will be appreciated by one of skill in the art, features of oneaspect or embodiment of the invention are also applicable to otheraspects or embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of one embodiment of the anode of thepresent invention comprising (a) a first layer 10 comprising lithiummetal, and (b) a multi-layer structure 21 comprising a single ionconducting layer 40, a polymer layer 30, and a single ion conductinglayer 41.

FIG. 2 shows a sectional view of one embodiment of the anode of thepresent invention comprising (a) a first layer 10 comprising lithiummetal, and (b) a multi-layer structure 20 comprising a polymer layer 30,a single ion conducting layer 40, and a polymer layer 31.

FIG. 3 shows a sectional view of one embodiment of the anode of thepresent invention comprising (a) a first layer 10 comprising lithiummetal, and (b) a multi-layer structure 22 comprising a polymer layer 30,a single ion conducting layer 40, metal layer 50, and a polymer layer31.

FIG. 4 shows a sectional view of one embodiment of the anode of thepresent invention comprising (a) a first layer 10 comprising lithiummetal, and (b) a multi-layer structure 23 comprising a polymer layer 30,a single ion conducting layer 40, a polymer layer 31, a single ionconducting layer 41, and a polymer layer 32.

FIG. 5 shows a sectional view of one embodiment of the anode of thepresent invention comprising (a) a first layer 10 comprising lithiummetal, (b) a surface reacted layer 60, and (c) a multi-layer structure24 comprising a single ion conducting layer 40, a polymer layer 30, asingle ion conducting layer 41, and a polymer layer 31.

FIG. 6 shows a sectional view of one embodiment of the anode of thepresent invention comprising (a) a substrate 70 and (b) a layer 80comprising lithium 15 co-deposited with a gaseous material 100.

FIG. 7 shows a sectional view of one embodiment of the anode of thepresent invention comprising (a) a substrate 70, (b) a first lithiumlayer 10, (c) a gaseous treatment layer 90, (c) a second lithium layer11, (d) a second gaseous treatment layer 91, and (e) a third lithiumlayer 12.

FIG. 8 shows a sectional view of one embodiment of the anode of thepresent invention comprising (a) a substrate 70, (b) a layer 86comprising lithium 15 co-deposited with a gaseous material 100, and (c)a gaseous treatment layer 90.

DETAILED DESCRIPTION OF THE INVENTION

The difficulties encountered by the reactivity of a lithium anodesurface of, for example, a Li/S electrochemical cell during storage orcycling, may, according to the present invention, be solved by the useof an anode comprising a multi-layer structure. The multi-layerstructure of the anode allows passage of lithium ions while acting as abarrier to other cell components more effectively, than single or duallayer interfacial films.

One aspect of the present invention pertains to an anode for use in anelectrochemical cell, wherein the anode comprises:

-   (i) a first anode active layer comprising lithium metal; and-   (ii) a multi-layer structure in contact with a surface of the first    layer; wherein the multi-layer structure comprises three or more    layers, wherein each of the layers comprises a single ion conducting    layer or a polymer layer.

The anode of the electrochemical cells of the present invention mayfurther comprise an intermediate layer between the first anode activelayer comprising lithium and the multilayer structure.

Anode Active Layers

The first layer of the anode of the present invention comprises lithiummetal as the anode active material. In one embodiment of the anodes ofthe present invention, the first anode active layer of the anode islithium metal. The lithium metal may be in the form of a lithium metalfoil or a thin lithium film that has been deposited on a substrate, asdescribed below. If desirable for the electrochemical properties of thecell, the lithium metal may be in the form of a lithium alloy such as,for example, a lithium-tin alloy or a lithium aluminum alloy.

The thickness of the first layer comprising lithium may vary from about2 to 200 microns. The choice of the thickness will depend on cell designparameters such as the excess amount of lithium desired, cycle life, andthe thickness of the cathode electrode. In one embodiment, the thicknessof the first anode active layer is in the range of about 2 to 100microns. In one embodiment, the thickness of the first anode activelayer is in the range of about 5 to 50 microns. In one embodiment, thethickness of the first anode active layer is in the range of about 5 to25 microns. In another embodiment, the thickness of the first anodeactive layer is in the range of about 10 to 25 microns.

The anodes of the present invention may further comprise a substrate, asis known in the art, in contact with a surface of the first anode activelayer on the side opposite to that of, for example, the multi-layerstructure, intermediate or temporary metal layer. Substrates are usefulas a support on which to deposit the first layer comprising the anodeactive material, and may provide additional stability for handling ofthin lithium film anodes during cell fabrication. Further, in the caseof conductive substrates, these may also function as a current collectoruseful in efficiently collecting the electrical current generatedthroughout the anode and in providing an efficient surface forattachment of the electrical contacts leading to the external circuit. Awide range of substrates are known in the art of anodes. Suitablesubstrates include, but are not limited to, those selected from thegroup consisting of metal foils, polymer films, metallized polymerfilms, electrically conductive polymer films, polymer films having anelectrically conductive coating, electrically conductive polymer filmshaving an electrically conductive metal coating, and polymer filmshaving conductive particles dispersed therein. In one embodiment, thesubstrate is a metallized polymer film. Examples of polymer filmsinclude, but are not limited to, polyethylene terephthalate (PET),polyethylene naphthalate (PEN), 1,4-cyclohexanedimethyleneterephthalate, polyethylene isophthalate, and polybutyleneterephthalate.

Another aspect of the anodes of the present invention pertains tomethods to deposit in-situ on a substrate anode-active layers comprisinglithium co-deposited with a gaseous material, such as, for example, CO₂or acetylene (C₂H₂), as described herein.

In one aspect of the anode of the present invention, the multi-layeredstructure of the present invention may be placed in direct contact witha surface of the first anode active layer comprising lithium. In anotherembodiment of the present invention, it may be desirable for the anodeactive layer to further comprise an intermediate layer interposedbetween a surface of the first anode active layer and a surface of themulti-layered structure. Such intermediate layers may, for example,comprise a temporary protective metal layer, or a layer formed from thereaction of CO₂, SO₂, or other reactive gaseous material with thelithium surface to provide either a temporary protective material layeror a permanent interfacial protective layer.

The difficulties encountered by the reactivity of a lithium surfaceduring deposition of, for example, anode stabilizing layers (ASL), may,according to the present invention, be solved by depositing over thelithium surface prior to coating or depositing such a stabilizing orother layer, a layer of a temporary protective material, such as, forexample, a temporary protective metal. The temporary protective materiallayer acts as a barrier layer to protect the lithium surface duringdeposition of other anode layers, such as during the deposition of themulti-layer structure of the present invention. Suitable temporaryprotective material layers include, but are not limited to, temporarymetal layers. Further, the temporary protective layer may allowtransportation of the lithium films from one processing station to thenext without undesirable reactions occurring at the lithium surfaceduring assembly of cells, or for solvent coating of layers onto theanode.

In one embodiment of the anode of the present invention, a layer of atemporary protective material may be placed in contact with the firstanode active layer comprising lithium metal on the side of the anodeactive layer facing the multi-layer structure. In one embodiment, thetemporary protective material is a temporary metal layer. The temporaryprotective metal is selected for its ability to form an alloy with,dissolve into, blend with, or diffuse into the lithium metal of thefirst layer comprising lithium metal. In one embodiment, the metal ofthe temporary protective layer is selected from the group consisting ofcopper, magnesium, aluminum, silver, gold, lead, cadmium, bismuth,indium, gallium, germanium, zinc, tin, and platinum. In a preferredembodiment the metal of the temporary protective metal layer is copper.

The thickness of the temporary protective metal layer interposed betweenthe first anode active layer and the multi-layer structure or otherlayer of the anode is selected to provide the necessary protection tothe layer comprising lithium, for example, during subsequent treatmentsto deposit other anode or cell layers, such as interfacial or protectivelayers. It is desirable to keep the layer thickness as thin as possiblewhile providing the desired degree of protection so as to not add excessamounts of non-active materials to the cell which would increase theweight of the cell and reduce its energy density. In one embodiment ofthe present invention, the thickness of the temporary protective layeris about 5 to 500 nanometers. In one embodiment of the presentinvention, the thickness of the temporary protective layer is about 20to 200 nanometers. In one embodiment of the present invention, thethickness of the temporary protective layer is about 50 to 200nanometers. In one embodiment of the present invention, the thickness ofthe temporary protective layer is about 100 to 150 nanometers.

During subsequent storage of an anode of this invention, comprising thefirst anode active layer and the temporary protective metal layer, orduring storage of an electrochemical cell into which an anode of thisinvention is assembled, or during electrochemical cycling of the cellcomprising an anode of the present invention, the temporary protectivemetal layer is capable of forming an alloy with, dissolving into,blending with, or diffusing into the lithium metal to yield a singleanode active layer comprising lithium metal. Lithium metal is known toalloy with certain metals as described herein, and has further beenobserved to diffuse or alloy with thin layers of certain other metalssuch as, for example, copper. The interdiffusion or alloying can beassisted by heating the anode assembly. Further it has been found thatalloying or diffusion of the temporary protective metal layer andlithium can be slowed or prevented by storage of the anode at lowtemperatures, such as at or below 0° C. This feature may be utilized inthe method of preparing anodes of the present invention.

According to another aspect of the present invention an intermediatelayer may be formed on a surface of an anode active layer comprisinglithium from the reaction of CO₂, SO₂, or other reactive gaseousmaterial, such as, for example, C₂H₂, with the lithium surface. In oneembodiment of the anode of the present invention, the intermediate layeris a plasma CO₂ treatment layer. In one embodiment, the plasma CO₂treatment layer is interposed between the first anode active layer andthe multi-layered structure of the anode.

Such layers may be formed by treating the surface of the anode activelayer, such as a lithium foil or a lithium film on a substrate, or maybe formed at the time of vacuum deposition of lithium vapor on asubstrate.

In an alternative approach, an interfacial layer may be formed duringthe vacuum deposition of lithium films on a substrate by co-depositingin situ lithium vapor and a reactive gaseous material. Such aco-deposition may result in an anode active layer 80 comprising lithium15 and a reaction product of the reactive gas and lithium 100 on asubstrate 70, as illustrated in FIG. 6.

In one embodiment of the present invention; the anode comprises: (a) ananode active layer comprising lithium metal co-deposited in-situ withone or more gaseous materials; and (b) a substrate. Suitable gaseousmaterial include, but are not limited to, said one or more materials areselected from the group consisting of carbon dioxide, acetylene,nitrogen, ethylene, sulfur dioxide, and hydrocarbons. Suitablesubstrates include those selected from the group consisting of metalfoils, polymer films, metallized polymer films, electrically conductivepolymer films, polymer films having an electrically conductive coating,electrically conductive polymer films having an electrically conductivemetal coating, and polymer films having conductive particles dispersedtherein. In one embodiment, anode further comprises a multi-layeredstructure in contact with a surface of the anode active layer, on theside opposite to the substrate.

Embodiments may be envisaged in which Li/CO₂/Li/CO₂/Li layers, as shownin FIG. 7, are built up by successive passes of the anode through theequipment.

The thickness of the intermediate or temporary protective layer, ifpresent as a discrete layer, is selected to provide the necessaryprotection to the layer comprising lithium, for example, duringsubsequent treatments to deposit other anode or cell layers, such asinterfacial or protective layers. It is desirable to keep the layerthickness as thin as possible while providing the desired degree ofprotection so as to not add excess amounts of non-active materials tothe cell which would increase the weight of the cell and reduce itsenergy density. Preferably, the thickness of the intermediate ortemporary protective layer is about 5 to 500 nanometers, and morepreferably is about 20 to 200 nanometers.

Methods to treat the anode active layer comprising lithium are notlimited to vapor or vacuum deposition techniques, and may includetreatment with reactive materials in the liquid or fluid state. Forexample, the surface of the anode active layer comprising lithium may betreated with supercritical fluid CO₂.

Although it is preferred to interpose the reactive intermediate layerbetween the anode active layer and the multi-layer structure, or todirectly deposit the multi-layered structure on the anode active layerformed by the co-deposition of lithium vapor and a reactive gaseousmaterial, in some instances an anode of the co-deposited anode activelayer or of the anode active layer and intermediate layer may be useddirectly in electrochemical cells without the multilayered structure andmay be beneficial to cell performance.

The anodes or anode active layers of the present invention, furthercomprising a temporary metal layer or other intermediate layer, such asCO₂ or SO₂ induced layers, are especially desirable when an interfaciallayer of some type is desired between the lithium surface and theelectrolyte. For example, when a single ion conducting layer is desiredat the lithium interface, it is preferable to deposit this directly onthe lithium surface. However, the precursors to or components of such aninterfacial layer may react with lithium to produce undesirableby-products or result in undesirable changes in the morphology of thelayers. By depositing a temporary protective metal layer or otherintermediate layer on the lithium surface prior to depositing theinterfacial layer such as the multi-layer structure of the presentinvention, side reactions at the lithium surface may be eliminated orsignificantly reduced. For example, when an interfacial film of alithium phosphorus oxynitride, as described in U.S. Pat. No. 5,314,765to Bates, is deposited in a nitrogen atmosphere by sputtering of Li₃PO₄onto a lithium surface, the nitrogen gas may react with lithium to formlithium nitride (LiN₃) at the anode surface. By depositing a layer of atemporary protective metal, for example, copper over the lithiumsurface, the interfacial layer may be formed without the formation oflithium nitride.

Multi-Layered Structure

The anodes of the present invention may comprise one or more single ionconducting layers or one or more polymer layers in contact with asurface of the first anode active layer, as described herein. Suchcombinations of single ion conducting or polymer layers that result in atotal of three or more layers are referred to herein as “multi-layeredstructures”. In the case of an intermediate layer, such as a temporaryprotective material layer, on the first anode active layer themulti-layer structure may not be in direct contact with the first anodeactive layer comprising lithium metal, but in contact with theintermediate layer.

In one embodiment of the present invention, where such an intermediatelayer is present, the anode comprises a third layer, which third layeris in contact with a second or intermediate layer, on the side oppositeto the first anode active layer, where the first anode active layercomprises lithium metal. In one embodiment, the second or intermediatelayer is a temporary protective metal layer. This third layer mayfunction as an interfacial layer, for example, as an anode stabilizingor as an anode protective layer between the anode active layer and theelectrolyte of the cell. In one embodiment, the third layer is a singleion conducting layer. In one embodiment, the third layer comprises apolymer. Other types of interfacial or protective layers may also bedeposited as a third layer, as are known in the art.

The thickness of the third layer of the anode of the present inventionmay vary over a wide range from about 5 nanometers to about 5000nanometers, and is dependent on the thickness of the layer required toprovide the desired beneficial effect of the layer while maintainingproperties needed for cell construction such as flexibility and lowinterfacial resistance. In one embodiment, the thickness of the thirdlayer is in the range of about 10 nanometers to 2000 nanometers. In oneembodiment, the thickness is in the range of about 50 nanometers to 1000nanometers. In one embodiment, the thickness is in the range of about100 nanometers to 500 nanometers.

The anode of the present invention may further comprise a fourth layerin contact with a surface of the third layer on the side opposite to theanode active layer or intermediate layer. A fourth layer may bedesirable when the components of the third layer, which functions tostabilize or protect the anode active layer comprising lithium, may beunstable to components present in the electrolyte. This fourth layershould be conductive to lithium ions, preferably nonporous to preventpenetration by electrolyte solvents, compatible with electrolyte and thethird layer, and flexible enough to accommodate for volume changes inthe layers occurring during discharge and charge. The fourth layershould further be insoluble in the electrolyte. As the fourth layer isnot directly in contact with the lithium layer, compatibility withmetallic lithium is not necessary. Examples of suitable fourth layersinclude, but are not limited to, organic or inorganic solid polymerelectrolytes, electrically and ionically conducting polymers, and metalswith certain lithium solubility properties. In one embodiment, thefourth layer comprises a polymer layer, wherein the fourth layer is incontact with the third layer on the side opposite to said second layer.In one embodiment, the polymer of the fourth layer is selected from thegroup consisting of electrically conductive polymers, ionicallyconductive polymers, sulfonated polymers, and hydrocarbon polymers.Further examples of suitable polymers for use in the fourth layer of thepresent invention are those described in U.S. patent application Ser.No. 09/399,967, now U.S. Pat. No. 6,183,901 B1, to Ying et al. of thecommon assignee for protective coating layers, the disclosures of whichare fully incorporated herein by reference.

The thickness of the fourth layer, which may be the outer layer of theanode layer, of the anode of the present invention is similar to that ofthe third layer and may vary over a wide range from about 5 to about5000 nanometers. The thickness of the fourth layer is dependent on thethickness of the layer required to provide the desired beneficial effectof the layer while maintaining properties needed for cell construction,such as flexibility, low interfacial resistance, and stability to theelectrolyte. In one embodiment, the thickness of the fourth layer is inthe range of about 10 nanometers to 2000 nanometers. In one embodiment,the thickness of the fourth layer is in the range of about 10 nanometersto 1000 nanometers. In one embodiment, the thickness of the fourth layeris in the range of about 50 nanometers to 1000 nanometers. In oneembodiment, the thickness of the fourth layer is in the range of about100 nanometers to 500 nanometers.

In a preferred embodiment of the present invention, the anode comprisesa multi-layered structure in contact with a surface of the first anodeactive layer comprising lithium metal, wherein the multi-layeredstructure comprises three or more layers, and wherein the multi-layeredstructure comprises one or more single ion conducting layers and one ormore polymer layers. Various embodiments of the present invention areillustrated in FIGS. 1-5, which are not drawn to scale. In oneembodiment, the multi-layered structure comprises alternating single ionconducting layers and polymer layers, as illustrated in Figures 1, 2,and 4.

For example, a three layer multi-layer structure may comprise a firstsingle ion conducting layer 40 in contact with a surface of the firstanode active layer comprising lithium metal 10, a polymer layer 30 incontact with a surface of the first single ion conducting layer 40, anda second single ion conducting layer 41 in contact with the surface ofthe polymer layer 30, as illustrated in FIG. 1.

More preferably, for example, a three layer multi-layer structure maycomprise a first polymer layer 30 in contact with a surface of the firstanode active layer comprising lithium metal 10, a single ion conductinglayer 40 in contact with the first polymer layer 30, and a secondpolymer layer 31 in contact with the single ion conducting layer 40, asillustrated in FIG. 2.

In one embodiment, the multi-layer structure comprises three or morelayers, wherein the multi-layered structure comprises one or more singleion conducting layers and one or more polymer layers. In anotherembodiment, the multi-layer structures comprise four or more layers,wherein the multi-layered structure comprises one or more single ionconducting layers and one or more polymer layers. In yet anotherembodiment, the multilayered structure comprises five or more layers, asillustrated in FIG. 4.

The thickness of the multi-layer structure of the present invention mayvary over a range from about 0.5 microns to about 10 microns. In apreferred embodiment, the thickness of the multi-layer structure mayrange from about 1 micron to about 5 microns.

The thickness of each layer of the multilayer structure of the anode ofthe present invention is similar to those of the third or fourth layerand may vary over a wide range from about 5 to about 5000 nanometers.The thickness of each layer is dependent on the thickness of the layerrequired to provide the desired beneficial effect of the layer whilemaintaining properties needed for cell construction, such asflexibility, low interfacial resistance, and stability to theelectrolyte. In one embodiment, the thickness of the each layer is inthe range of about 10 nanometers to 2000 nanometers. In one embodiment,the thickness of each layer is in the range of about 10 nanometers to1000 nanometers. In one embodiment, the thickness of the each layer isin the range of about 50 nanometers to 1000 nanometers. In oneembodiment, the thickness of each layer is in the range of about 100nanometers to 500 nanometers.

The single ion conductivity of each layer of the multilayer may varyover a wide range. Preferably, the single ion conductivity of each layeris greater than 10 ⁻⁷ ohm⁻¹cm⁻¹. However, when very thin layers are usedthe ion conductivity may less.

Suitable single ion conducting layers for use in the anodes of thepresent invention include, but are not limited to, inorganic, organic,and mixed organic-inorganic polymeric materials. The term “single ionconducting layer,” as used herein, pertains to a layer which selectivelyor exclusively allows passage of singly charged cations. Single ionconducting layers have the capability of selectively or exclusivelytransporting cations, such as lithium ions, and may comprise polymerssuch as, for example, disclosed in U.S. Pat. No. 5,731,104 to Ventura,et al. In one embodiment, the single ion conducting layer comprises asingle ion conducting glass conductive to lithium ions. Among thesuitable glasses are those that may be characterized as containing a“modifier” portion and a “network” portion, as known in the art. Themodifier is typically a metal oxide of the metal ion conductive in theglass. The network former is typically a metal chalcogenide, such as forexample, a metal oxide or sulfide.

Preferred single ion conducting layers for use in the anodes of thepresent invention include, but are not limited to, glassy layerscomprising a glassy material selected from the group consisting oflithium silicates, lithium borates, lithium aluminates, lithiumphosphates, lithium phosphorus oxynitrides, lithium silicosulfides,lithium germanosulfides, lithium lanthanum oxides, lithium titaniumoxides, lithium borosulfides, lithium aluminosulfides, and lithiumphosphosulfides, and combinations thereof. In one embodiment, the singleion conducting layer comprises a lithium phosphorus oxynitride.Electrolyte films of lithium phosphorus oxynitride are disclosed, forexample, in U.S. Pat. No. 5,569,520 to Bates. A thin film layer oflithium phosphorus oxynitride interposed between a lithium anode and anelectrolyte is disclosed, for example, in U.S. Pat. No. 5,314,765 toBates. The selection of the single ion conducting layer will bedependent on a number of factors including, but not limited to, theproperties of electrolyte and cathode used in the cell.

Suitable polymer layers for use in the anodes of the present invention,include, but are not limited to, those selected from the groupconsisting of electrically conductive polymers, ionically conductivepolymers, sulfonated polymers, and hydrocarbon polymers. The selectionof the polymer will be dependent on a number of factors including, butnot limited to, the properties of electrolyte and cathode used in thecell. Suitable electrically conductive polymers include, but are notlimited to, those described in U.S. Pat. No. 5,648,187 to Skotheim, forexample, including, but not limited to, poly(p-phenylene),polyacetylene, poly(phenylenevinylene), polyazulene,poly(perinaphthalene), polyacenes, and poly(naphthalene-2,6-diyl).Suitable ionically conductive polymers include, but are not limited to,ionically conductive polymers known to be useful in solid polymerelectrolytes and gel polymer electrolytes for lithium electrochemicalcells, such as, for example, polyethylene oxides. Suitable sulfonatedpolymers include, but are not limited to, sulfonated siloxane polymers,sulfonated polystyrene-ethylene-butylene polymers, and sulfonatedpolystyrene polymers. Suitable hydrocarbon polymers include, but are notlimited to, ethylene-propylene polymers, polystyrene polymers, and thelike.

Also preferred for the polymer layers of the multi-layered structure ofthe present invention, are crosslinked polymer materials formed from thepolymerization of monomers including, but are not limited to, alkylacrylates, glycol acrylates, polyglycol acrylates, polyglycol vinylethers, polyglycol divinyl ethers, and those described in U.S. patentapplication Ser. No. 09/399,967, now U.S. Pat. No. 6,183,901 B1, to Yinget al. of the common assignee for protective coating layers forseparator layers, the disclosures of which are fully incorporated hereinby reference. For example, one such crosslinked polymer material ispolydivinyl poly(ethylene glycol). The crosslinked polymer materials mayfurther comprise salts, for example, lithium salts, to enhance ionicconductivity. In one embodiment, the polymer layer of the multi-layeredstructure comprises a crosslinked polymer. In one embodiment, a polymerlayer is formed from the polymerization of one or more acrylate monomersselected from the group consisting of alkyl acrylates, glycol acrylates,and polyglycol acrylates.

The outer layer of the multi-layered structure, i.e. the layer that isin contact with the electrolyte or separator layer of the cell, shouldbe selected for properties such as protection of underlying layers whichmay be unstable to components present in the electrolyte. This outerlayer should be conductive to lithium ions, preferably nonporous toprevent penetration by electrolyte solvents, compatible with electrolyteand the underlying layers, and flexible enough to accommodate for volumechanges in the layers observed during discharge and charge. The outerlayer should further be stable and preferably insoluble in theelectrolyte.

Examples of suitable outer layers include, but are not limited to,organic or inorganic solid polymer electrolytes, electrically andionically conducting polymers, and metals with certain lithiumsolubility properties. In one embodiment, the polymer of the outer layeris selected from the group consisting of electrically conductivepolymers, ionically conductive polymers, sulfonated polymers, andhydrocarbon polymers. Further examples of suitable polymers for use inthe outer layer of the present invention are those described in U.S.patent application Ser. No. 09/399,967, now U.S. Pat. No. 6,183,901 B1,to Ying et al. of the common assignee for protective coating layers ofcoated separators.

In one embodiment of the present invention, the multi-layer structuremay further comprise a metal alloy layer. The term “metal alloy layer,”as used herein, pertains to lithiated metal alloy layers. The lithiumcontent of the metal alloy layer may vary from about 0.5% by weight toabout 20% by weight, depending, for example, on the specific choice ofmetal, the desired lithium ion conductivity, and the desired flexibilityof the metal alloy layer. Suitable metals for use in the metal alloylayer include, but are not limited to, Al, Zn, Mg, Ag, Pb, Cd, Bi, Ga,In, Ge, and Sn. Preferred metals are, Zn, Mg, Sn, and Al. In oneembodiment, the metal alloy comprises a metal selected from the groupconsisting of Zn, Mg, Sn, and Al.

The thickness of the metal alloy layer may vary over a range from about10 nm to about 1000 nm (1 micron). In one embodiment, the thickness ofthe metal alloy layer is about 10 to 1000 nanometers. In one embodiment,the thickness of the metal alloy layer is about 20 to 500 nanometers. Inone embodiment, the thickness of the metal alloy layer is about 20 to500 nanometers. In one embodiment, the thickness of the metal alloylayer is about 50 to 200 nanometers.

The metal alloy layer may be placed between polymer layers, between ionconducting layers, or between an ion conducting layer and a polymerlayer, as illustrated in FIG. 3. For example, in FIG. 3 a multi-layerstructure is shown comprising (a) a first layer 10 comprising lithiummetal, and (b) a multi-layer structure 22 comprising a polymer layer 30,a single ion conducting layer 40, metal layer 50, and a polymer layer31. In one embodiment, the metal alloy layer is interposed between apolymer layer and an ion-conducting layer or two polymer layers, or twoion-conducting layers. In one embodiment, the metal alloy layer is theouter layer of the multi-layered structure.

The anode of the present invention may have the multi-layer structurecomprising three or more layers in contact with a surface of the firstanode active layer comprising lithium metal, or in contact with asurface of a second or intermediate temporary protective metal layer, orin contact with a surface or intermediate layer on the first anodeactive layer, such as, for example, from reaction with CO₂ or SO₂. Inone embodiment of the present invention, the multi-layer structure isformed on a surface of the first anode active layer comprising lithiummetal. In one embodiment of the present invention, a multi-layerstructure is formed on a surface of an intermediate layer on the sideopposite to the anode active layer. In one embodiment of the presentinvention, a layer from the reaction of the first anode active layercomprising lithium metal with CO₂ or SO2 is interposed between themulti-layer structure and the first anode active layer comprisinglithium metal, wherein the multi-layer structure is formed on a surfaceof the reacted layer 60, as illustrated in FIG. 5.

Multi-layer structures of the present invention possess propertiessuperior to those of the individual layers which comprise themulti-layer. Each of the layers of the multi-layer structure, forexample, the single ion conducting layers, the polymer layers, and themetal alloy layers, possess desirable properties but at the same timepossess certain undesirable properties. For example, single ionconducting layers, especially vacuum deposited single ion conductinglayers, are flexible as thin films but as they become thicker growdefects, such as pinholes and rougher surfaces. Metal alloy layers, forexample, may block liquid and polysulfide migration, and are veryductile and flexible in thin film form but may interdiffuse with lithiumand are electron conducting. Polymer layers and especially crosslinkedpolymer layers, for example, can provide very smooth surfaces, addstrength and flexibility, and may be electron insulating. In themulti-layer structures of the present invention comprising three or morelayers comprising one or more single ion conducting layers and one ormore polymer layers, and optionally one or more metal alloy layers, itis possible to obtain essentially defect free structures. For example, acrosslinked polymer layer deposited over a single ion conducting layermay smooth the surface and thereby minimize defects in subsequent singleion conducting layers deposited upon it. The crosslinked polymer layermay be viewed as decoupling defects in layers on either side of it.Although the multi-layer structures consisting of three layers areeffective in defect reduction of the anode interfacial layer, additionalbenefit may be gained from four. or more layers. The benefits of adefect free layer or structure include efficient exclusion ofundesirable species from the lithium surface, which can lead to dendriteformation, self discharge, and loss of cycle life. Other benefits of themulti-layer structure include an increased tolerance of the volumetricchanges which accompany the migration of lithium back and forth from theanode during the cycles of discharge and charge of the cell, andimproved robustness to withstand stresses during manufacturingprocesses.

The anodes of the present invention may be assembled into cells bycombining with an electrolyte and a cathode comprising a cathode activematerial, as described herein. The anodes may also be formed with otheralkali or alkaline earth metal anode active materials by suitable choiceof the multi-layered structure, and if desired by the presence of atemporary protective metal layer or other intermediate layer between theanode active layer and the multi-layered structure.

Methods of Making Anodes

Another aspect of the present invention pertains to a method ofpreparing an anode for use in an electrochemical cell, wherein the anodecomprises: (i) a first anode active layer comprising lithium metal; and(ii) a multi-layer structure in contact with a surface layer of thefirst anode active layer; wherein the multi-layer structure comprisesthree or more layers, wherein each of the layers comprises a single ionconducting layer or a polymer layer, as described herein.

In one embodiment, the method of making an anode for an electrochemicalcell comprises the steps of:

-   (a) depositing onto a substrate a first anode active layer    comprising lithium metal, or providing a lithium metal foil as a    first anode active layer;-   (b) depositing over the first anode active layer a first layer    comprising a polymer or a single ion conducting layer;-   (c) depositing over the first layer of step (b) a second layer    comprising a single ion conducting layer if the layer of step (b) is    a polymer, or a polymer layer if the layer of step (b) is a single    ion conducting layer; and-   (d) depositing over the second layer of step (c) a third layer    comprising a single ion conducting layer if the layer of step (c) is    a polymer, or a polymer layer if the layer of step (c) is a single    ion conducting layer to form an anode comprising:    -   (i) a first anode active layer comprising lithium metal; and    -   (ii) a multi-layer structure in contact with a surface layer of        the first anode active layer; wherein the multi-layer structure        comprises three or more layers, wherein each of the layers        comprises a single ion conducting layer or a polymer layer.

The order of the deposition of the polymer and single ion conductinglayer will depend on the desired properties of the multi-layeredstructure. It may also be desirable to deposit two or more polymerlayers or two or more single ion conducting layers that are in contactwith each other. A metal alloy layer may be deposited subsequent to step(b). Such a metal alloy layer may be deposited between a polymer layerand a single ion conducting layer or between two polymer layers, orbetween two single ion conducting layers. A metal alloy layer may alsobe deposited as the outer most layer of the multi-layer structure.

Another aspect of the present invention pertains to a method ofpreparing an anode for use in an electrochemical cell, wherein the anodecomprises:

-   (i) a first anode active layer comprising lithium metal; and-   (ii) a multi-layer structure in contact with a surface layer of the    first anode active layer; wherein the multi-layer structure    comprises three or more layers, wherein each of said layers    comprises a single ion conducting layer or a polymer layer, and is    formed by the method comprising the steps of:-   (a) depositing onto a substrate a first anode active layer    comprising lithium metal, or alternatively, providing a lithium    metal foil as a first anode active layer;-   (b) depositing over the first anode active layer a polymerizable    monomer layer;-   (c) polymerizing the monomer layer of step (b) to form a first    polymer layer;-   (d) depositing over the polymer layer of step (c) a first single ion    conducting layer;-   (e) depositing over the first single ion conducting layer of    step (d) a second polymerizable monomer layer; and-   (f) polymerizing the monomer layer of step (e) to form a second    polymer layer to form a multi-layer structure comprising a single    ion conducting layer and two polymer layers.

The methods of the present invention may further comprise, subsequent tostep (a) and prior to step (b), the step of treating the first anodeactive layer comprising lithium metal with CO₂ or SO² or other gaseousmaterial, or depositing a layer of a temporary protective material, suchas a temporary protective metal, as described herein.

The method of the present invention may further comprise, subsequent tostep (f), repeating the steps (d), or (d), (e) and (f) one or more timesto form a multi-layer structure comprising four or more layers.

Similarly, multi-layered structures may be formed by depositing over afirst anode active layer a first layer of a single ion conducting layer,followed by a first polymer layer, and subsequently a second ionconducting layer.

If a metal alloy layer is desired in the multi-layered structure, thismay be deposited after any one of steps (c), (d), or (f).

As described herein, the polymer layers are preferably cross-linkedpolymer layers. In one embodiment, the polymer layers of saidmulti-layer structure comprise a polymer layer formed from thepolymerization of one or more acrylate monomers selected from the groupconsisting of alkyl acrylates, glycol acrylates, and polyglycolacrylates.

In the method of the present invention, the polymerizable monomer layerof steps (b) and (e) may comprise dissolved lithium salts. Otheradditives, such as, for example, uv-curing agents, may also be added tothe polymerizable monomer layer.

In another embodiment of the methods of the present invention forpreparing an anode for use in an electrochemical cell, wherein the anodecomprises:

-   (i) a first anode active layer comprising lithium metal; and-   (ii) a multi-layer structure in contact with a surface layer of the    first anode active layer; wherein the multi-layer structure    comprises three or more layers, wherein each of said layers    comprises a single ion conducting layer or a polymer layer; the    method comprises the steps of:-   (a) depositing onto a substrate a first anode active layer    comprising lithium metal, or alternatively, providing a lithium    metal foil as a first anode active layer;-   (b) depositing over the first anode active layer a first polymer    layer;-   (c) depositing over the polymer layer of step (b) a first single ion    conducting layer; and-   (d) depositing over the first single ion conducting layer of    step (c) a second polymer layer to form a multi-layer structure    comprising a single ion conducting layer and two polymer layers.

In the method of the present invention, the polymer layer of steps (b)and (d) may comprise dissolved lithium salts. If a metal alloy layer isdesired in the multi-layer structure, this may be deposited after step(c) or later step. Preferable, the polymer layers are cross-linkedpolymer layers.

Another aspect of the present invention pertains to a method ofpreparing an anode active layer comprising a temporary protective layeror intermediate layer for use in an electrochemical cell, wherein theanode active layer is formed by the steps of:

-   (a) depositing onto a substrate a first anode active layer    comprising lithium metal, or alternatively, providing a lithium    metal foil as a first anode active layer; and-   (b) depositing over the first anode active layer a temporary    protective layer or intermediate layer.

Alternatively, step (b) may comprise treating or reacting the surface ofthe first anode active layer comprising lithium or lithium foil with areactive gaseous material, such as, for example CO₂. In one embodimentof the methods of the present invention, the anode active layercomprising lithium is treated with a CO₂ plasma.

Another aspect of the present invention pertains to a method ofpreparing an anode active layer comprising a temporary protective metallayer for use in an electrochemical cell, wherein the anode active layeris formed by the steps of:

-   (a) depositing onto a substrate a first anode active layer    comprising lithium metal, or alternatively, providing a lithium    metal foil as a first anode active layer; and-   (b) depositing over the first anode active layer a second layer of a    temporary protective metal, wherein the temporary protective metal    is selected from the group consisting of copper, magnesium,    aluminum, silver, gold, lead, cadmium, bismuth, indium, gallium,    germanium, zinc, tin, and platinum; and wherein the temporary    protective metal is capable of forming an alloy with lithium metal    or diffusing into lithium metal.

The method of forming an anode active layer comprising a temporaryprotective layer of the present invention, may further comprise afterstep (b), a step (c) of depositing a third layer over the second layerformed in step (b), wherein the third layer comprises a single ionconducting layer, as described herein, or a polymer, as describedherein. The method may further comprise after step (c), a step (d) ofdepositing a fourth layer over the third layer, wherein the fourth layercomprises a polymer. Further polymer or single ion conducting layers maybe deposited to form a multi-layer structure as described herein.

The layers of the anode of the present invention may be deposited by anyof the methods known in the art, such as physical or chemical vapordeposition methods, extrusion, and electroplating. Examples of suitablephysical or chemical vapor deposition methods include, but are notlimited to, thermal evaporation (including, but not limited to,resistive, inductive, radiation, and electron beam heating), sputtering(including, but not limited to, diode, DC magnetron, RF, RF magnetron,pulsed, dual magnetron, AC, MF, and reactive), chemical vapordeposition, plasma enhanced chemical vapor deposition, laser enhancedchemical vapor deposition, ion plating, cathodic arc, jet vapordeposition, and laser ablation. Many vacuum apparatus designs anddeposition processes have been described for the deposition of materialson polymer films. For example, Witzman et al., in U.S. Pat. No.6,202,591 B1, and references cited therein describe apparatus andcoating process for the deposition of materials on polymer films.

Preferably the deposition of the layers of the anode of the presentinvention are carried out in a vacuum or inert atmosphere to minimizeside reactions in the deposited layers which would introduce impuritiesinto the layers or which may affect the desired morphology of thelayers. It is preferable that anode active layer and the layers of themulti-layered structure are deposited in a continuous fashion in amultistage deposition apparatus. If the anode active layer comprises atemporary protective metal layer, this layer is capable of providingprotection for the anode active layer if the layers of the multi-layeredstructure are deposited in a different apparatus.

Suitable methods for depositing the temporary protective metal layerinclude, but are not limited to, thermal evaporation, sputtering, jetvapor deposition, and laser ablation. In one embodiment, the temporaryprotective metal layer is deposited by thermal evaporation orsputtering.

The layers of the multi-layered structure comprising a single ionconducting layer or a polymer layer may be deposited from eitherprecursor moieties or from the material of the layer, as known in theart for forming such materials.

In one embodiment, the single ion conducting layer is deposited by amethod selected from the group consisting of sputtering, electron beamevaporation, vacuum thermal evaporation, laser ablation, chemical vapordeposition, thermal evaporation, plasma enhanced chemical vacuumdeposition, laser enhanced chemical vapor deposition, and jet vapordeposition.

In one embodiment, the polymer layer is deposited by a method selectedfrom the group consisting of electron beam evaporation, vacuum thermalevaporation, laser ablation, chemical vapor deposition, thermalevaporation, plasma assisted chemical vacuum deposition, laser enhancedchemical vapor deposition, jet vapor deposition, and extrusion. Thepolymer layer may also be deposited by spin-coating methods or flashevaporation methods. Flash evaporation methods are particularly usefulfor deposition of crosslinked polymer layers.

A preferred method for deposition of crosslinked polymer layers is aflash evaporation method, for example, as described in U.S. Pat. No.4,954,371 to Yializis. A preferred method for deposition of crosslinkedpolymer layers comprising lithium salts is a flash evaporation method,for example, as described in U.S. Pat. No 5,681,615 to Affinito et al.

Preferred methods for the deposition of the first anode active layercomprising lithium metal on to a substrate are those selected from thegroup consisting of thermal evaporation, sputtering, jet vapordeposition, and laser ablation. In one embodiment, the first layer isdeposited by thermal evaporation. Alternatively, the first anode activelayer may comprise a lithium foil, or a lithium foil and a substrate,which may be laminated together by a lamination process as known in theart, to form the first layer.

In another aspect of the present invention, the anode active layercomprising lithium may be formed by co-depositing in-situ lithium withone or more gaseous materials onto a substrate. The term “co-deposited,”as used herein, pertains to a process in which gaseous material orreaction products of gaseous material and lithium, are deposited in-situonto a substrate with lithium. Co-deposition may be different from firstdepositing and cooling a lithium film and then post-treating bydepositing another layer or reacting with another gaseous material. Theterm “gaseous material,” as used herein, pertains to a material which isin the form of a gas under the conditions of temperature and pressure atwhich the deposition occurs. For example, a material may be a liquid atambient temperature and pressure, but be in gaseous form underconditions of vapor deposition.

In one embodiment of the present invention, lithium vapor from thedeposition source is co-deposited on the substrate in presence of agaseous material. In one embodiment, lithium vapor from a depositionsource is co-deposited on a substrate in the presence of a material froma plasma or from an ion gun. In one embodiment, lithium vapor from thedeposition source is condensed onto the substrate and the depositedlithium immediately treated with a gaseous material. In one embodiment,lithium vapor from the deposition source is co-deposited on thesubstrate in presence of a gaseous material and the deposited lithiumimmediately treated with a gaseous material. In another embodiment ofthe present invention, the method employs multiple depositions oflithium vapor, each co-deposited in the presence of a gaseous materialby means of multiple passes of the substrate by the deposition source.

Suitable gaseous materials include but are not limited to carbondioxide, acetylene, nitrogen, ethylene, sulfur dioxide, andhydrocarbons. Suitable materials for co-deposition from a plasma sourceinclude, but are not limited to, carbon dioxide, acetylene, nitrogen,ethylene, sulfur dioxide, hydrocarbons, alkyl phosphate esters, alkylsulfite esters, and alkyl sulfate esters. Preferred gaseous materialsare carbon dioxide and acetylene. Most preferred gaseous material iscarbon dioxide. The amount of gaseous material co-deposited with thelithium may vary over a wide range. Preferably the amount of the gaseousmaterial co-deposited with the lithium is between 0.2% and 5.0% byweight of the lithium. Higher amounts of gaseous material may result inundesirable insulative deposits of carbonaceous materials on the lithiumsurface.

The anode active layers formed by the co-deposition in-situ of lithiumand a gaseous material may be deposited by methods such as, for example,physical deposition methods and plasma assisted deposition methods. Theco-deposition of the gaseous material may be accomplished, for example,by introduction of the gaseous material adjacent to the lithium sourcein the deposition chamber.

While not wishing to be bound by theory, it is believed thatco-deposition of lithium with gaseous material, for example carbondioxide or acetylene, incorporates carbonaceous material in and/or onthe deposited lithium. Carbon dioxide can form a number of products uponreaction with lithium. For example, Zhuang et al., in Surface Science,1998, 418, 139-149, report that the interaction of carbon dioxide withclean lithium at 320° K produces a mixture of species includingelemental carbon, a limited amount of CO22-(carbonate), and O2- (oxide).It is noted that the exact composition and ratio of products istemperature dependent. The co-deposition processes of lithium and carbondioxide may produce a lithium layer with a surface layer comprisingelemental carbon, oxide, and carbonate. The co-deposition processes oflithium and carbon dioxide may produce a lithium layer in whichelemental carbon, oxide, and carbonate are intimately dispersed or theco-deposition process may produce both intimately dispersed elementalcarbon, oxide, and carbonate and a surface layer comprising thesecomponents.

The co-deposition process(es) provide suitable methods for the formationof a surface layer formed on the first anode active layer comprisinglithium from the reaction of, for example CO₂, which is interposedbetween the multi-layer structure and the first anode active layercomprising lithium.

Electrochemical Cells

The anodes of the present invention, as described herein, may be used inboth primary and secondary lithium cells of a variety of chemistries.

In one embodiment, the anode of the electrochemical cells of the presentinvention comprises a co-deposited lithium anode active layer formedin-situ by the co-deposition of lithium and a gaseous material, asdescribed herein.

In one aspect, the present invention provides an electrochemical cellcomprising:

-   (a) a cathode comprising a cathode active material;-   (b) an anode; and-   (c) a non-aqueous electrolyte interposed between the anode and the    cathode, wherein the anode comprises:    -   (i) a first anode active layer comprising lithium metal, as        described herein; and    -   (ii) a multi-layer structure, as described herein, in contact        with a surface layer of the first layer; wherein the multi-layer        structure comprises three or more layers wherein each of the        three or more layers comprises a layer selected from the group        consisting of single ion conducting layers and polymer layers.

In a preferred embodiment, the cathode comprises an electroactivesulfur-containing material.

In one embodiment, the first anode active layer of the cell furthercomprises an intermediate layer, wherein the intermediate layer isinterposed between the first anode active layer and the multi-layeredstructure. In one embodiment, the intermediate layer is selected fromthe group consisting of temporary protective metal layers and plasma CO₂treatment layers.

In one embodiment, the first anode active layer is a co-depositedlithium anode active layer, as described herein.

In another aspect, the present invention provides an electrochemicalcell comprising:

-   (a) a cathode comprising a cathode active material;-   (b) an anode; and-   (c) a non-aqueous electrolyte interposed between the cathode and the    anode;    wherein the anode comprises an anode active layer, which anode    active layer comprises:    -   (i) a first layer comprising lithium metal;    -   (ii) a second layer of a temporary protective material, as        described herein, in contact with a surface of said first layer;        and    -   (iii) a multi-layer structure in contact with a surface of the        second layer.

In one embodiment, the present invention provides an electrochemicalcell comprising:

-   (a) a cathode comprising a cathode active material;-   (b) an anode; and-   (c) a non-aqueous electrolyte interposed between the cathode and the    anode.    wherein the anode comprises an anode active layer, which anode    active layer comprises:    -   (i) a first layer comprising lithium metal;    -   (ii) a second layer of a temporary protective metal in contact        with a surface of the first layer; and    -   (iii) a multi-layer structure in contact with a surface of the        second layer;

wherein the temporary protective metal is capable of forming an alloywith lithium metal or is capable of diffusing into lithium metal.

In one embodiment, the metal of the temporary protective layer isselected from the group copper, magnesium, aluminum, silver, gold, lead,cadmium, bismuth, indium, gallium, germanium, zinc, tin, and platinum.

The temporary protective metal layer of the anode active layer may alloywith, diffuse with, dissolve into, blend with, or diffuse into with thelithium metal of the first layer prior to the electrochemical cyclingcell or during the electrochemical cycling of a cell.

Suitable cathode active materials for use in the cathode of theelectrochemical cells of the present invention include, but are notlimited to, electroactive transition metal chalcogenides, electroactiveconductive polymers, and electroactive sulfur-containing materials, andcombinations thereof. As used herein, the term “chalcogenides” pertainsto compounds that contain one or more of the elements of oxygen, sulfur,and selenium. Examples of suitable transition metal chalcogenidesinclude, but are not limited to, the electroactive oxides, sulfides, andselenides of transition metals selected from the group consisting of Mn,V, Cr, Ti, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re,Os, and Ir. In one embodiment, the transition metal chalcogenide isselected from the group consisting of the electroactive oxides ofnickel, manganese, cobalt, and vanadium, and the electroactive sulfidesof iron. In one embodiment, the cathode active layer comprises anelectroactive conductive polymer. Examples of suitable electroactiveconductive polymers include, but are not limited to, electroactive andelectronically conductive polymers selected from the group consisting ofpolypyrroles, polyanilines, polyphenylenes, polythiophenes, andpolyacetylenes. Preferred conductive polymers are polypyrroles,polyanilines, and polyacetylenes.

The term “electroactive sulfur-containing material,” as used herein,relates to cathode active materials which comprise the element sulfur inany form, wherein the electrochemical activity involves the breaking orforming of sulfur-sulfur covalent bonds. Suitable electroactivesulfur-containing materials, include, but are not limited to, elementalsulfur and organic materials comprising sulfur atoms and carbon atoms,which may or may not be polymeric. Suitable organic materials includethose further comprising heteroatoms, conductive polymer segments,composites, and conductive polymers.

In one embodiment, the sulfur-containing material, in its oxidized form,comprises a polysulfide moiety, S_(m), selected from the groupconsisting of covalent -S_(m)-moieties, ionic -S_(m) ⁻moieties, andionic S_(m) ²⁻moieties, wherein m is an integer equal to or greater than3. In one embodiment, m of the polysulfide moiety, S_(m), of thesulfur-containing polymer is an integer equal to or greater than 6. Inone embodiment, m of the polysulfide moiety, S_(m), of thesulfur-containing polymer is an integer equal to or greater than 8. Inone embodiment, the sulfur-containing material is a sulfur-containingpolymer. In one embodiment, the sulfur-containing polymer has a polymerbackbone chain and the polysulfide moiety, S_(m), is covalently bondedby one or both of its terminal sulfur atoms as a side group to thepolymer backbone chain. In one embodiment, the sulfur-containing polymerhas a polymer backbone chain and the polysulfide moiety, S_(m), isincorporated into the polymer backbone chain by covalent bonding of theterminal sulfur atoms of the polysulfide moiety.

In one embodiment, the electroactive sulfur-containing materialcomprises greater than 50% by weight of sulfur. In a preferredembodiment, the electroactive sulfur-containing material comprisesgreater than 75% by weight of sulfur. In a more preferred embodiment,the electroactive sulfur-containing material comprises greater than 90%by weight of sulfur.

The nature of the electroactive sulfur-containing materials useful inthe practice of this invention may vary widely, as known in the art.

In one embodiment, the electroactive sulfur-containing materialcomprises elemental sulfur. In one embodiment, the electroactivesulfur-containing material comprises a mixture of elemental sulfur and asulfur-containing polymer.

Examples of sulfur-containing polymers include those described in: U.S.Patent Nos. 5,601,947 and 5,690,702 to Skotheim et al.; U.S. Pat. Nos.5,529,860 and 6,117,590 to Skotheim etal.; and U.S. patent applicationSer. No. 08/995,122, now U.S. Pat. No. 6,201,100, to Gorkovenko et al.of the common assignee and PCT Publication No. WO 99/33130. Othersuitable electroactive sulfur-containing materials comprisingpolysulfide linkages are described in U.S. Pat. No. 5,441,831 toSkotheim et al.; U.S. Pat. No. 4,664,991 to Perichaud et al., and inU.S. Pat. Nos. 5,723,230, 5,783,330, 5,792,575 and 5,882,819 to Naoi etal. Still further examples of electroactive sulfur-containing materialsinclude those comprising disulfide groups as described, for example in,U.S. Pat. No. 4,739,018 to Armand et al.; U.S. Pat. Nos. 4,833,048 and4,917,974, both to De Jonghe et al.; U.S. Pat. Nos. 5,162,175 and5,516,598, both to Visco et al.; and U.S. Pat. No. 5,324,599 to Oyama etal.

The cathodes of the cells of the present invention may further compriseone or more conductive fillers to provide enhanced electronicconductivity. Examples of conductive fillers include, but are notlimited to, those selected from the group consisting of conductivecarbons, graphites, activated carbon fibers, non-activated carbonnanofibers, metal flakes, metal powders, metal fibers, carbon fabrics,metal mesh, and electrically conductive polymers. The amount ofconductive filler, if present, is preferably in the range of 2 to 30% byweight of the cathode active layer. The cathodes may also furthercomprise other additives including, but not limited to, metal oxides,aluminas, silicas, and transition metal chalcogenides.

The cathodes of the cells of the present invention may also comprise abinder. The choice of binder material may vary widely so long as it isinert with respect to the other materials in the cathode. Useful bindersare those materials, usually polymeric, that allow for ease ofprocessing of battery electrode composites and are generally known tothose skilled in the art of electrode fabrication. Examples of usefulbinders include, but are not limited to, those selected from the groupconsisting of polytetrafluoroethylenes (Teflon®), polyvinylidenefluorides (PVF₂ or PVDF), ethylene-propylene-diene (EPDM) rubbers,polyethylene oxides (PEO), UV curable acrylates, UV curablemethacrylates, and heat curable divinyl ethers, and the like. The amountof binder, if present, is preferably in the range of 2 to 30% by weightof the cathode active layer.

The cathodes of the cells of the present invention may further comprisea current collector as is known in the art. Current collectors areuseful in efficiently collecting the electrical current generatedthroughout the cathode and in providing an efficient surface forattachment of the electrical contacts leading to the external circuit aswell as functioning as a support for the cathode. Examples of usefulcurrent collectors include, but are not limited to, those selected fromthe group consisting of metallized plastic films, metal foils, metalgrids, expanded metal grids, metal mesh, metal wool, woven carbonfabric, woven carbon mesh, non-woven carbon mesh, and carbon felt.

Cathodes of the cells of the present invention may be prepared bymethods known in the art. For example, one suitable method comprises thesteps of: (a) dispersing or suspending in a liquid medium theelectroactive sulfur-containing material, as described herein; (b)optionally adding to the mixture of step (a) a conductive filler,binder, or other cathode additives; (c) mixing the composition resultingfrom step (b) to disperse the electroactive sulfur-containing material;(d) casting the composition resulting from step (c) onto a suitablesubstrate; and (e) removing some or all of the liquid from thecomposition resulting from step (d) to provide the cathode.

Examples of suitable liquid media for the preparation of the cathodes ofthe present invention include aqueous liquids, non-aqueous liquids, andmixtures thereof. Especially preferred liquids are non-aqueous liquidssuch as, for example, methanol, ethanol, isopropanol, propanol, butanol,tetrahydrofuran, dimethoxyethane, acetone, toluene, xylene,acetonitrile, and cyclohexane.

Mixing of the various components can be accomplished using any of avariety of methods known in the art, so long as the desired dissolutionor dispersion of the components is obtained. Suitable methods of mixinginclude, but are not limited to, mechanical agitation, grinding,ultrasonication, ball milling, sand milling, and impingement milling.

The formulated dispersions can be applied to substrates by any of avariety of coating methods known in the art and then dried usingtechniques, known in the art, to form the solid cathodes of the lithiumcells of this invention. Suitable hand coating techniques include, butare not limited to, the use of a wire-wound coating rod or gap coatingbar. Suitable machine coating methods include, but are not limited to,the use of roller coating, gravure coating, slot extrusion coating,curtain coating, and bead coating. Removal of some or all of the liquidfrom the mixture can be accomplished by any of a variety of means knownin the art. Examples of suitable methods for the removal of liquid fromthe mixture include, but are not limited to, hot air convection, heat,infrared radiation, flowing gases, vacuum, reduced pressure, and bysimply air drying.

The method of preparing the cathodes of the present invention mayfurther comprise heating the electroactive sulfur-containing material toa temperature above its melting point and then resolidifying the meltedelectroactive sulfur-containing material to form a cathode active layerhaving a reduced thickness and a redistributed sulfur-containingmaterial of higher volumetric density than before the melting process.

The electrolytes used in electrochemical or battery cells function as amedium for the storage and transport of ions, and in the special case ofsolid electrolytes and gel electrolytes, these materials mayadditionally function as a separator between the anode and the cathode.Any liquid, solid, or gel material capable of storing and transportingions may be used, so long as the material is electrochemically andchemically unreactive with respect to the anode and the cathode, and thematerial facilitates the transport of lithium ions between the anode andthe cathode. The electrolyte must also be electronically non-conductiveto prevent short circuiting between the anode and the cathode.

Typically, the electrolyte comprises one or more ionic electrolyte saltsto provide ionic conductivity and one or more non-aqueous liquidelectrolyte solvents, gel polymer materials, or polymer materials.Suitable non-aqueous electrolytes for use in the present inventioninclude, but are not limited to, organic electrolytes comprising one ormore materials selected from the group consisting of liquidelectrolytes, gel polymer electrolytes, and solid polymer electrolytes.Examples of non-aqueous electrolytes for lithium batteries are describedby Dominey in Lithium Batteries, New Materials, Developments andPerspectives, Chapter 4, pp. 137-165, Elsevier, Amsterdam (1994).Examples of gel polymer electrolytes and solid polymer electrolytes aredescribed by Alamgir et al. in Lithium Batteries, New Materials,Developments and Perspectives, Chapter 3, pp. 93-136, Elsevier,Amsterdam (1994). In one embodiment of the cells of the presentinvention, the non-aqueous electrolyte is a liquid electrolyte.

Examples of useful non-aqueous liquid electrolyte solvents include, butare not limited to, non-aqueous organic solvents, such as, for example,N-methyl acetamide, acetonitrile, acetals, ketals, esters, carbonates,sulfones, sulfites, sulfolanes, aliphatic ethers, cyclic ethers, glymes,polyethers, phosphate esters, siloxanes, dioxolanes,N-alkylpyrrolidones, substituted forms of the foregoing, and blendsthereof. Fluorinated derivatives of the foregoing are also useful asliquid electrolyte solvents.

Liquid electrolyte solvents are also useful as plasticizers for gelpolymer electrolytes. Examples of useful gel polymer electrolytesinclude, but are not limited to, those comprising one or more polymersselected from the group consisting of polyethylene oxides, polypropyleneoxides, polyacrylonitriles, polysiloxanes, polyimides, polyphosphazenes,polyethers, sulfonated polyimides, perfluorinated membranes (NAFION™resins), polydivinyl polyethylene glycols, polyethylene glycoldiacrylates, polyethylene glycol dimethacrylates, derivatives of theforegoing, copolymers of the foregoing, crosslinked and networkstructures of the foregoing, and blends of the foregoing, andoptionally, one or more plasticizers.

Examples of useful solid polymer electrolytes include, but are notlimited to, those comprising one or more polymers selected from thegroup consisting of polyethers, polyethylene oxides, polypropyleneoxides, polyimides, polyphosphazenes, polyacrylonitriles, polysiloxanes,derivatives of the foregoing, copolymers of the foregoing, crosslinkedand network structures of the foregoing, and blends of the foregoing.

In addition to electrolyte solvents, gelling agents, and polymers asknown in the art for forming non-aqueous electrolytes, the non-aqueouselectrolyte may further comprise one or more ionic electrolyte salts,also as known in the art, to increase the ionic conductivity.

Examples of ionic electrolyte salts for use in the electrolytes of thepresent invention include, but are not limited to, LiSCN, LiBr, LiI,LiClO₄, LiAsF₆, LiSO₃CF₃, LiSO₃CH₃, LiBF₄, LiB(Ph)₄, LiPF₆,LiC(SO₂CF₃)₃, and LiN(SO₂CF₃)₂. Other electrolyte salts. useful in thepractice of this invention include lithium polysulfides (Li₂S_(x)), andlithium salts of organic ionic polysulfides (LiS_(x)R)_(n), where x isan integer from 1 to 20, n is an integer from 1 to 3, and R is anorganic group, and those disclosed in U.S. Pat. No. 5,538,812 to Lee etal. Preferred ionic electrolyte salts are LiBr, LiI, LiSCN, LiBF₄,LiPF₆, LiAsF₆, LiSO₃CF₃, LiN(SO₂CF₃)₂, and LiC(SO₂CF₃)₃.

The electrochemical cells of the present invention may further comprisea separator interposed between the cathode and anode. Typically, theseparator is a solid non-conductive or insulative material whichseparates or insulates the anode and the cathode from each otherpreventing short circuiting, and which permits the transport of ionsbetween the anode and the cathode.

The pores of the separator may be partially or substantially filled withelectrolyte. Separators may be supplied as porous free standing filmswhich are interleaved with the anodes and the cathodes during thefabrication of cells. Alternatively, the porous separator layer may beapplied directly to the surface of one of the electrodes, for example,as described in PCT Publication No. WO 99/33125 to Carlson et al. and inU.S. Pat. No. 5,194,341 to Bagley et al.

A variety of separator materials are known in the art. Examples ofsuitable solid porous separator materials include, but are not limitedto, polyolefins, such as, for example, polyethylenes and polypropylenes,glass fiber filter papers, and ceramic materials. Further examples ofseparators and separator materials suitable for use in this inventionare those comprising a microporous xerogel layer, for example, amicroporous pseudo-boehmite layer, which may be provided either as afree standing film or by a direct coating application on one of theelectrodes, as described in U.S. patent application Ser. No. 08/995,089,now U.S. Pat. No. 6,153,337, and U.S. patent application Ser. No.09/215,112 by Carlson et al. of the common assignee, the disclosures ofwhich are fully incorporated herein by reference. Solid electrolytes andgel electrolytes may also function as a separator in addition to theirelectrolyte function.

In one embodiment, the solid porous separator is a porous polyolefinseparator. In one embodiment, the solid porous separator comprises amicroporous xerogel layer. In one embodiment, the solid porous separatorcomprises a microporous pseudo-boehmite layer.

Battery cells of the present invention may be made in a variety of sizesand configurations as known to those skilled in the art. These batterydesign configurations include, but are not limited to, planar,prismatic, jelly roll, w-fold, stacked, and the like.

The electrochemical cells comprising the anodes of the present inventionmay be either primary or secondary batteries or cells.

Another aspect of the present invention pertains to a method of formingan electrochemical cell, the method comprising the steps of: (i)providing a cathode; (ii) providing an anode, as described herein; and,(iii) interposing an electrolyte between the anode and the cathode.

EXAMPLES

Several embodiments of the present invention are described in thefollowing examples, which are offered by way of illustration and not byway of limitation.

Example 1

A vacuum web coating system located in a dry room, having an unwinddrive, liquid cooled drum at −20° C., load cell rollers for controllingtension, a rewind drive, and two deposition zones, was loaded with ananode substrate of 23μm PET metallized on one side with 60 nm of inconeland of 15 cm width. The chamber was evacuated to 10⁻⁶ Torr. Lithium wasdeposited on to the substrate by first heating a thermal evaporationlithium source to 535° C. to allow significant evaporation, and thenstarting the web drive at 0.5 feet per minute. The lithium evaporationwas allowed to stabilize to give an 25μm coating of lithium on theinconel of the substrate layer.

Example 2

A vacuum web coating system located in a dry room, having an unwinddrive, liquid cooled drum at −20° C., load cell rollers for controllingtension, a rewind drive, and two deposition zones, was loaded with ananode substrate of 23μm PET metallized on one side with 60 nm of inconeland of 15 cm width. The chamber was evacuated to 10⁻⁶ Torr. Lithium wasdeposited on to the substrate by first heating a thermal evaporationlithium source to 535° C. to allow significant evaporation, and thenstarting the web drive at 0.5 feet per minute. The lithium evaporationwas allowed to stabilize to give an 25μm coating of lithium on theinconel of the substrate layer. Immediately adjacent to the lithiumsource CO₂ was introduced through a mass flow controller at a flowbetween 10 and 100 sccm raising the pressure to 0.1 to 50 mTorr. Darkdiscoloration was immediately seen in the co-deposited lithium with CO₂from this in situ deposition process.

Example 3

A vacuum web coating system located in a dry room, having an unwinddrive, liquid cooled drum at −20° C., load cell rollers for controllingtension, a rewind drive, and two deposition zones, was loaded with ananode substrate of 23μm PET metallized on one side with 60 nm of inconeland of 15 cm width. The chamber was evacuated to 10⁻⁶ Torr. Lithium wasdeposited on to the substrate by first heating a thermal evaporationlithium source to 535° C. to allow significant evaporation, and thenstarting the web drive at 0.5 feet per minute. The lithium evaporationwas allowed to stabilize to give an 25μm coating of lithium on theinconel of the substrate layer. Immediately adjacent to the lithiumsource RF magnetron plasma treatment with the CO₂ gas was performed.Forward RF power was between 50 and 100 W at a pressure of 0.1 to 50mTorr. Dark discoloration was immediately seen in the co-depositedlithium with CO₂ from this in situ deposition process.

Example 4

A vacuum web coating system located in a dry room, having an unwinddrive, liquid cooled drum at −20° C., load cell rollers for controllingtension, a rewind drive, and two deposition zones, was loaded with ananode substrate of 23μm PET metallized on one side with 60 nm of inconeland of 15 cm width. The chamber was evacuated to 10⁻⁶ Torr. Lithium wasdeposited on to the substrate by first heating a thermal evaporationlithium source to 535° C. to allow significant evaporation, and thenstarting the web drive at 0.5 feet per minute. The lithium evaporationwas allowed to stabilize to give an 25μm coating of lithium on theinconel of the substrate layer. Immediately adjacent to the lithiumsource acetylene was introduced through a mass flow controller at a flowbetween 10 and 100 sccm raising the pressure to 0.1 to 50 mTorr. Darkdiscoloration was immediately seen in the co-deposited lithium withacetylene from this in situ deposition process.

Example 5

A vacuum web coating system located in a dry room, having an unwinddrive, liquid cooled drum at −20° C., load cell rollers for controllingtension, a rewind drive, and two deposition zones, was loaded with ananode substrate of 23μm PET metallized on one side with 60 nm of inconeland of 15 cm width. The chamber was evacuated to 10⁻⁶ Torr. Lithium wasdeposited on to the substrate by first heating a thermal evaporationlithium source to 535° C. to allow significant evaporation, and thenstarting the web drive at 0.5 feet per minute. The lithium evaporationwas allowed to stabilize to give an 25μm coating of lithium on theinconel of the substrate layer. Upon completion of the deposition thelithium coated substrate was re-wound on the unwind drive while thevacuum was maintained in the apparatus. With the lithium source off, thelithium coated substrate was subjected to RF magnetron plasma treatmentwith the CO₂ gas. Forward RF power was between 50 and 100 W at apressure of 0.1 to 50 mTorr. The post treated lithium had a darkappearance.

Example 6

In situ co-deposited lithium with CO₂ was made by the method of Example2. While still in the vacuum apparatus a 100 nm thick layer of Lipon wasdeposited on the surface of the co-deposited lithium by a RF sputteringsource using a Li₃PO₄ target and 5 mTorr .of N₂ with 1000 W forwardpower.

Example 7

Small flat cells were assembled in the following way. A compositecathode was prepared by coating a 3.68 cm wide cathode active layer on a4.19 cm wide Al/PET substrate. A cathode slurry was prepared from 70parts by weight of elemental sulfur (available from Aldrich ChemicalCompany, Milwaukee, WI), 15 parts by weight of Printex XE-2 (a tradename for conductive carbon available from Degussa Corporation, Akron,OH), 10 parts by weight of graphite (available from Fluka/Sigma-Aldrich,Milwaukee, WI), 4 parts by weight of TA22-8 resin, and 1 part by weightof lonac PFAZ-322. The solids content of the slurry was 14% by weight ina solvent mixture of 80% isopropanol, 12% water, 5% 1-methoxy-2-propanoland 3% dimethylethanolamine (on a weight basis). The slurry was coatedby a slot die coater onto both sides of the substrate. The coating wasdried in the ovens of the slot die coater. The resulting dry cathodeactive layer had a thickness of about 20 microns on each side of thecurrent collector, with a loading of electroactive cathode material ofabout 1.15 mg/cm². 4.5 cm lengths of this composite cathode were used inbuilding cells.

Lithium anodes of 10 cm in length and 4.19 cm in width were cut from theanode material of Example I Small flat cells were assembled by foldingthe anode around the cathode with a porous separator, 10μm E25 SETELA (atrademark for a polyolefin separator available from Tonen ChemicalCorporation, Tokyo, Japan, and also available from Mobil ChemicalCompany, Films Division, Pittsford, NY) separator, inserted betweenanode and cathode. The cell was secured with ¼″ wide polyimide tape andplaced into a bag (package material consisting of polymer coatedAluminum foil available from Sealrite Films, San Leandro, CA). 0.4mL ofa 1.4 M solution of lithium bis(trifluoromethylsulfonyl)imide, (lithiumimide, available from 3M Corporation, St. Paul, MN) in a 42:58 volumeratio mixture of 1,3-dioxolane and dimethoxyethane, was added aselectrolyte and the cell was vacuum sealed. Testing was performed at adischarge current of 0.42 mA/cm² to a voltage of 1.5V and charged at acurrent 0.24 mA/cm² to 110% last half cycle capacity.

The discharge capacity at the 5^(th) cycle was 24 mAh and at the 40^(th)cycle was 22 mAh. The specific discharge capacity at the 40^(th) cyclewas 514 mAh/g and at the 100^(th) cycle was 375 mAh/g.

Example 8

Small flat cells were made by the method of Example 7, except thatco-deposited lithium anode material of Example 2 was used in place oflithium anode material of Example 1. Charging and discharging wasperformed as in Example 7.

The discharge capacity at the 5^(th) cycle was 28 mAh and at the 40^(th)cycle was 23 mAh. The specific discharge capacity at the 40^(th) cyclewas 556 mAh/g and at the 100^(th) cycle was 432 mAh/g. The specificdischarge capacity at 100 cycles was 115 % of the specific dischargecapacity of Example 7.

Example 9

Small flat cells were made by the method of Example 7, except thatco-deposited lithium anode material of Example 4 was used in place oflithium anode material of Example 1. Charging and discharging wasperformed as in Example 7.

The discharge capacity at the 5 ^(th) cycle was 27 mAh and at the40^(th) cycle was 24 mAh.

Example 10

Small flat cells were made by the method of Example 7, except thatco-deposited lithium anode material of Example 5 was used in place oflithium anode material of Example 1. Charging and discharging wasperformed as in Example 7.

Example 11

Small flat cells were made by the method of Example 7, except thatco-deposited lithium anode material of Example 6 was used in place oflithium anode material of Example 1. Charging and discharging wasperformed as in Example 7.

The specific discharge capacity at the 40 ^(th) cycle was 585 mAh/g andat the 100^(th) cycle was 456 mAh/g. The specific discharge capacity at100 cycles was 121% of the specific discharge capacity of Example 7.

Example 12

A cathode with coated separator for making small flat cells was made asfollows. A cathode was prepared by coating a mixture of 65 parts ofelemental sulfur, 15 parts of a conductive carbon pigment PRINTEX XE-2,15 parts of a graphite pigment (available from Fluka Chemical Company,Ronkonkoma, NY), and 5 parts of fumed silica CAB-O-SIL EH-5 (a tradenamefor silica pigment available from Cabot Corporation, Tuscola, IL)dispersed in isopropanol onto a 17 micron thick conductive carbon coatedaluminum coated PET substrate (available from Rexam Graphics, SouthHadley, MA). After drying and calendering, the coated cathode activelayer thickness was about 15-18 microns.

A coating mixture comprising 86 parts by weight (solid content) ofDISPAL 11N7-12 (a trademark for boehmite sol available from CONDEA VistaCompany, Houston, TX), 6 parts by weight (solid content) of AIRVOL 125(a trademark for polyvinyl alcohol polymer available from Air Products,Inc., Allentown, PA), 3 parts by weight of polyethylene oxide (900,000MW from Aldrich Chemical Company, Milwaukee, WI) and 5 parts by weightpolyethylene oxide dimethylether, M-250, (Fluka Chemical Company,Ronkonkoma, NY) in water was prepared. This coating mixture was coateddirectly on the cathode active layer above, followed by drying at 130°C.

A 5% by weight solution of a 3:2 ratio by weight of CD 9038 (a tradenamefor ethoxylated bisphenol A diacrylate, available from Sartomer Inc.,Exton, PA) and CN 984 (a tradename for a urethane acrylate availablefrom Sartomer Inc., Exton, PA) was prepared by dissolving thesemacromonomers in ethyl acetate. To this solution, 0.2% by weight (basedon the total weight of acrylates) of ESCURE KTO (a tradename for aphotosensitizer available from Sartomer Inc., Exton, PA) was added, and5% by weight of CAB-O-SIL TS-530 (a trademark for a fumed silica pigmentavailable from Cabot Corporation, Tuscola, IL) which was dispersed inthe solution by sonication. This solution was coated onto thepseudo-boehmite coated cathode and dried to form the protective coatinglayer. The thickness of the pigmented protective coating layer was about4 microns. The dried film was then cured by placing it on the conveyorbelt of a FUSION Model P300 UV exposure unit (available from FusionSystems Company, Torrance, CA) and exposing it to the UV lamps for 30seconds to form a cured protective coating layer.

An anode for making small flat cells was made from commercial 50μmlithium foil.

Small flat cells were made by the method of Example 7 from the separatorcoated cathode and lithium foil but using 0.3 g of electrolyte. Testingwas performed at a discharge current of 0.42 mA/cm² to a voltage of 1.5V and charged at a current 0.24 mA/cm² for 5 hours or to a voltage of2.8 V.

The initial discharge capacity of the cells was 40 mAh which dropped to20 mAh at 105 cycles.

Example 13

Small flat cells were made by the method of Example 12 except that thelithium anode foil was replaced by a CO₂ treated lithium foil. Thetreated foil was made by suspending a lithium foil of 50μm thickness insuper critical fluid (scf) CO₂ at 45° C. and 100 atmospheres for 1 hourto produce a scf CO₂ treated lithium anode material. The testing wasperformed by the method of Example 12.

The initial discharge capacity of the cells was 40 mAh which dropped to20 mAh at 245 cycles. The cells made from the scf CO₂ treated lithiumanode showed more than a 130% increase in cycle life compared with cellshaving the untreated lithium anodes of Example 12.

Example 14

A vacuum web coating system located in a dry room, having an unwinddrive, liquid cooled drum, load cell rollers for controlling tension, arewind drive, and two deposition zones, was loaded with an anodesubstrate of 23μm PET metallized on one side with 100 nm of copper. Thechamber was evacuated to 10⁻⁶ Torr. Lithium was deposited on to thesubstrate by first heating a thermal evaporation Li source to 550° C. toallow significant evaporation, and then starting the web drive at 1.2feet per minute. The lithium evaporation was allowed to stabilize togive an 8μm coating of lithium on the copper of the substrate layer(PET/Cu/Li). The DC magnetron sputtering source zone, positioned afterthe lithium source, was brought up to 2.4 mTorr while bringing thelithium evaporation zone only up to 10⁻⁵ torr. The sputtering source wasgiven 2 kW power and copper was deposited on top of the lithium layer toa thickness of either 120, 60 or 30 nm to give a composite anode ofPET/Cu/Li/Cu. The web was removed from the coating system in the dryroom.

A PET/Cu/Li/Cu composite anode, with a 120 nm temporary copperprotective layer and a comparative PET/Cu/Li anode were tested forreactivity to isopropyl alcohol by placing a sample in a dish andcovering it with alcohol. While the lithium without the copper temporaryprotective coating reacted quickly, the temporary protective coppercoated lithium was observed not to significantly react.

Visual observations of lithium/Cu layers showed that lithium with a 120nm temporary copper protective layer was stable for storage overnightunder vacuum at room temperature. When this sample was heated in an ovenat about 90° C., the pink coloration of the copper layer disappeared asthe copper and lithium layers inter-diffused, alloyed, or mixed. Asimilar sample placed in a freezer at about −15° C. still retained itspink color after 11 months. Samples with copper layers of 30 or 60 nm ofcopper were less stable, with the copper coloration disappearing afterstorage overnight.

Example 15

Three copper protected lithium anodes were formed by coating copper ontothe lithium surface of a PET/copper/lithium anode structure as describedin Example 14. The thickness of the coated copper layers on the outersurface of the lithium were 30, 60 and 120 nanometers. The copperprotected lithium anodes were stored at room temperature overnight.

Small flat cells were assembled from the copper protected lithium anodes(PET/copper/lithium/copper) or uncoated PET/copper/lithium anodes as acontrol, with a cathode prepared by coating a mixture of 75 parts ofelemental sulfur (available from Aldrich Chemical Company, Milwaukee,WI), 15 parts of a conductive carbon pigment PRINTEX XE-2 (a trademarkfor a carbon pigment available from Degussa Corporation, Akron, OH), and10 parts of PYROGRAF-III (a tradename for carbon filaments availablefrom Applied Sciences, Inc., Cedarville, OH) dispersed in isopropanolonto one side of a 17 micron thick conductive carbon coated aluminumfoil substrate (Product No. 60303 available from Rexam Graphics, SouthHadley, MA). After drying, the coated cathode active layer thickness wasabout 30 microns and the loading of sulfur in the cathode active layerwas 1.07 mg/cm². The electrolyte was a 1.4 M solution of lithiumbis(trifluoromethylsulfonyl)imide, (lithium imide, available from 3MCorporation, St. Paul, MN) in a 40:55:5 volume ratio mixture of1,3-dioxolane, dimethoxyethane, and tetraethyleneglycol divinylether.The porous separator used was 16 micron E25 SETELA (a trademark for apolyolefin separator available from Tonen Chemical Corporation, Tokyo,Japan, and also available from Mobil Chemical Company, Films Division,Pittsford, NY). The active area of the cathode and anode in the smallflat cells was 25 cm².

The assembled cells were stored for 2 weeks at room temperature duringwhich the impedance was periodically measured. The high frequencyimpedance (175 KHz) was found to be equal for both the control cells andthe cells with copper protected lithium surfaces, irrespective of thethickness of the copper protective layer, and was representative of theconductivity of the electrolyte in the porous Tonen separator, about10.9 ohm Cm².

Initial measurements of the low frequency impedance (80 Hz) was observedto be different for the control and copper protected lithium anodes, andwas dependent on the thickness of the copper protective layer andstorage time. Storage time measurements showed that the cells with a 30nm copper protective layer had a impedance 20% higher than the controlcell, while the impedance was 200% higher for cells with 60 nm copperprotective layers and 500% higher for cells with 120 nm copperprotective layers. The impedance for fresh control cells was around 94ohm cm².

During storage of the cells with copper protected lithium, the impedancedecreased and became equal to that of the control cells in two days forcells for 30 nm Cu, in 5 days for cells with 60 nm Cu, and in 14 daysfor cells with 120 nm Cu protective layers.

After storage, all cells were discharged at a current density of 0.4mA/cm² and a voltage cutoff 1.25 V. The delivered capacities were foundto be equal for the control cells and the cells with temporary copperprotective layers, showing that the temporary Cu layers disappeared inabout two weeks and did not prevent electrochemical cycling or reducethe cell performance.

While the invention has been described in detail and with reference tospecific and general embodiments thereof, it will be apparent to oneskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope thereof.

1. An electrode for use in an electrochemical cell, comprising: a baseelectrode material comprising lithium; a single-ion conductive materiallayer; a polymer layer between the base electrode material and thesingle-ion-conductive material layer; and a temporary protective metallayer or a plasma treatment layer between the base electrode materialand the polymer layer.
 2. An electrode as in claim 1, further comprisinga second single-ion-conductive material layer on the first polymerlayer, and a second polymer layer on the second single-ion-conductivematerial layer.
 3. An electrode as in claim 1, wherein the single-ionconductive material is a metal.
 4. An electrode as in claim 1, whereinthe single-ion conductive material has a thickness of no greater than 5microns.
 5. An electrode as in claim 1, wherein the polymer layer has athickness of no greater than 5 microns.
 6. An electrode as in claim 1,wherein the temporary protective metal layer has a thickness of nogreater than 200 nanometers.
 7. An electrode as in claim 1, wherein themulti-layer structure further comprises a metal alloy layer formedbetween the non-electronically conductive single-ion conducting layerand the polymer layer.
 8. An electrode as in claim 7, wherein the metalalloy layer comprises a metal selected from the group consisting of Zn,Mg, Sn, and Al.
 9. An electrode as in claim 1 comprising more than onesingle-ion conductive material layers and more than one polymer layers,the polymer layers interspersed between the single-ion conductivematerial layers.
 10. An electrode as in claim 1 comprising more than onemetal layers.
 11. An electrode as in claim 1, wherein the thickness ofthe single-ion conductive material layer is no greater than 5 microns,and the thickness of the polymer layer is no greater than 5 microns. 12.An electrode as in claim 1, wherein the single-ion conductive materiallayer is non-electronically conducting.
 13. An electrode as in claim 1,comprising a temporary protective metal layer between the base electrodematerial and the polymer layer.
 14. An electrode as in claim 1,comprising a plasma treatment layer between the base electrode materialand the polymer layer.
 15. An electrochemical cell comprising: (a) acathode comprising an electroactive sulfur-containing material; (b) ananode; and (c) an electrolyte interposed between said anode and saidcathode, wherein said anode comprises: (i) a first anode active layercomprising lithium metal; (ii) a multi-layer structure in contact with asurface layer of said first anode active layer, wherein said multi-layerstructure comprises three or more layers, wherein at least one of saidthree or more layers comprises a single-ion conducting layer and atleast another one of said three or more layers comprises a polymerlayer, wherein said first anode active layer further comprises anintermediate layer selected from the group consisting of temporaryprotective metal layers and plasma treatment layers, wherein saidintermediate layer is interposed between said first anode active layerand said multi-layered structure.
 16. An electrochemical cell of claim15, wherein the multi-layer structure comprises four or more layers. 17.An electrochemical cell of claim 15, wherein the multi-layer structurefurther comprises a metal alloy layer formed between thenon-electronically conductive single-ion conducting layer and thepolymer layer.
 18. An electrochemical cell of claim 17, wherein themetal alloy layer comprises a metal selected from the group consistingof Zn, Mg, Sn, and Al.
 19. An electrochemical cell of claim 15, whereinthe intermediate layer is a plasma treatment layer.
 20. Anelectrochemical cell of claim 15, wherein the intermediate layer is atemporary protective metal layer.
 21. An electrochemical cell of claim20, wherein the temporary protective metal layer comprises a metalselected from the group consisting of copper, magnesium, aluminum,silver, gold, lead, cadmium, bismuth, indium, gallium, germanium, zinc,tin, and platinum.
 22. An electrochemical cell of claim 20, wherein thetemporary protective metal layer has a thickness of no greater than 200nanometers.
 23. An electrochemical cell of claim 15, wherein thesingle-ion conducting layer is non-electronically conducting.
 24. Anelectrochemical cell comprising: (a) a cathode comprising anelectroactive sulfur-containing material; (b) an anode; and (c) anelectrolyte interposed between said anode and said cathode, wherein saidanode comprises: (i) a first anode active layer comprising an alkali oralkali earth metal; (ii) a multi-layer structure in contact with asurface layer of said first anode active layer, wherein said multi-layerstructure comprises three or more layers, wherein at least one of saidthree or more layers comprises a single-ion conducting layer and atleast another one of said three or more layers comprises a polymerlayer, wherein said first anode active layer further comprises anintermediate layer selected from the group consisting of temporaryprotective metal layers and plasma treatment layers, wherein saidintermediate layer is interposed between said first anode active layerand said multi-layered structure.
 25. An electrochemical cell of claim24, wherein the single-ion conducting layer is non-electronicallyconducting.
 26. An electrochemical cell of claim 24, wherein theintermediate layer is a plasma treatment layer.
 27. An electrochemicalcell of claim 24, wherein the intermediate layer is a temporaryprotective metal layer.
 28. An electrochemical cell of claim 24, whereinthe multi-layer structure comprises four or more layers.
 29. Anelectrode for use in an electrochemical cell, comprising: a baseelectrode material comprising lithium; an ionically conductive metallayer; a polymer layer between the base electrode material and theionically conductive metal layer; and a temporary protective metal layeror a plasma treatment layer between the base electrode material and thepolymer layer.
 30. An electrode as in claim 29 comprising more than oneionically conductive metal layers and more than one polymer layers, thepolymer layers interspersed between the ionically conductive metallayers.
 31. An electrode as in claim 29, comprising a temporaryprotective metal layer between the base electrode material and thepolymer layer.
 32. An electrode as in claim 29, comprising a plasmatreatment layer between the base electrode material and the polymerlayer.
 33. An electrode as in claim 29, wherein the ionically conductivemetal layer comprises a metal selected from the group consisting of Zn,Mg, Sn, and Al.
 34. An electrochemical cell comprising: (a) a cathodecomprising an electroactive sulfur-containing material; (b) an anode;and (c) an electrolyte interposed between said anode and said cathode,wherein said anode comprises: (i) a first anode active layer comprisinglithium metal; and (ii) a multi-layer structure in contact with asurface layer of said first anode active layer, wherein said multi-layerstructure comprises three or more layers, wherein at least one of saidthree or more layers comprises a non-electronically conductingsingle-ion conducting layer and at least another one of said three ormore layers comprises a polymer layer.